As a sealed fluid under varying pressure or high pressure is more frequently applied to machineries in recent years, how to reduce a leak amount of the sealed fluid in the mechanical seal device draws more attentions. Leak of the sealed fluid which is caused by the way of the mechanical seal device being installed has been a major concern. In particular, a leak of the sealed fluid from a pair combination of the seal rings is caused by an installation structure of a gasket which provides a seal between the mating surfaces of the installation gap which is created when one of the seal rings is installed in a seal housing. Especially a complex displacement may occur to the seal surface of the seal ring which is retained by a gasket which is made of rubber-like elastic material when it is subjected to high pressure or varying pressure of the sealed fluid. For example, in order to provide a seal between the seal housing and one member of the seal rings which is mounted relative to the seal housing, when a rubber-made gasket in “L”-shape cross section which is installed between these members is strongly urged by the other member of the paired seal rings which oppose each other or urged by the high pressure of the sealed fluid, a conventional construction allows the gasket to undergo elastic deformation with the one member of the seal rings in the axial direction. Prior art related to the current technique, for instance, can be found in Patent Reference 1 given below. Thus the respective seal surfaces of the pair of seal rings undergo a slight relative displacement in the urging direction of the external force acted onto the pair of seal rings. As a consequence, this slight displacement of the seal surfaces causes the sealed fluid to leak through between the seal surfaces.
Furthermore, since the gasket in “L” shape cross section fully occupies between the seal housing and the seal ring installed relative to the seal housing, frictional heat of the seal ring which is generated in sliding movement can hardly be transferred to the seal housing. This causes an accumulation of the generated heat in the sliding movement within the seal ring, thereby possibly causing a thermal stress to the seal ring. This thermal stress may induce cracking on the seal surface of the seal ring or cause deformation of the seal surface. Moreover, the frictional heat generated in the seal ring causes a fatigue in the gasket sealing between the seal ring and the seal housing, thereby being unable to provide a support to the seal ring as well as causing degradation of seal performance such as a leak of the sealed fluid from the contact interface of the gasket.
FIG. 11 illustrates a mechanical seal device 100 employed as a shaft seal device in an industrial pump. This mechanical seal device 100 has a similar construction to FIG. 3 in Patent Reference 1 given below though a gasket 110 has a different construction. The right-hand side portion of FIG. 11 which is omitted has a similar arrangement to FIG. 3 shown in Patent Reference 1. The mechanical seal device 100 depicted in FIG. 11 shows a half cut-away, partial cross-section view along the axial direction while the seal device is mounted in the shaft. This mechanical seal device 100 is arranged to combine a stationary seal portion 100A with a rotary seal portion 100B. The stationary seal portion 100A in cooperation with the rotary seal portion 100B prevents a leak of the inboard sealed fluid to the outboard side “A” in which the stationary seal portion 100A is mounted between a through bore of the seal housing 160 and a rotary shaft 160 which is inserted into the through bore.
A stationary seal ring 102 in the stationary seal portion 100A is securely attached by means of a gasket 110 which is installed between the stationary seal ring 102 and the seal housing 160. This gasket 110 provides a seal between the fit surfaces of both members after being installed between the seal housing 160 and the stationary seal ring 102. The gasket 110 then has a first rubber layer 110C adhering to the inner circumference of a reinforcement annulus 111. Also a second rubber layer 110D is adhered to the outer circumference of the reinforcement annulus 111. One end portion of the reinforcement annulus 111 at the inboard side is covered with a thin layer of rubber, which defines a thrust end portion 110A. Both of the other end portions of the first rubber layer 110C and the second rubber layer 110D define rubber end portions 110B which form almost the same surface level as a metal end portion 111A.
Axial length of the gasket 110 is arranged to be more or less the same as the axial length of the stationary seal ring 102. The inner circumferential surface of the gasket 110 forms a secure engagement with the outer circumferential surface of the stationary seal ring 102 while the outer circumferential surface 110D1 of the gasket 110 forms a secure engagement surface 160C of the seal housing 160. When this gasket 110 is inserted, the rubber end portion 110B and the back surface 102B of the stationary seal ring 102 are aligned to form the same surface level so as to abut a support surface 160A of the seal housing 160. And a stationary seal surface 102A is disposed at another end surface of the stationary seal ring 102 opposite the back surface 102B.
On the other hand, the rotary seal portion 100B opposing the stationary seal portion 100A is arranged in a similar manner to the one shown in the figures of Patent Reference 1. That is, it is comprised of a rotary seal ring 120, a bellows, not shown, for sealing between the rotary seal ring 120 and the rotary shaft 150, and a coiled spring, not shown, for exerting a resilient urging force to the rotary seal ring 120.
As described earlier, this mechanical seal device 100 securely seals the sealed fluid by means of a seal-tight contact between the stationary seal surface 102A of the stationary seal ring 102 and the rotary seal surface 120A of the rotary seal ring 120 for preventing the fluid from leaking to the outboard side “A”. Furthermore a clearance gap between the seal housing 160 and the stationary seal ring 102 is tightly sealed by means of the gasket 110 in order to prevent the sealed fluid from leaking to the outboard side “A” through the clearance gap. When the stationary seal surface 102A and the rotary seal surface 120A undergo relative sliding movement under a seal-tight contact state between the two seal surfaces 102A, 120A, the both surfaces 102A, 120A start to generate heat as the sliding movement continues. In particular, in case of a sealed fluid containing impurities or being a chemical liquid, the seal surfaces are also heated due to the presence of the sealed fluid containing impurities therebetween.
In the mechanical seal device 100 thus constructed, the stationary seal ring 102 is mounted onto a fit engagement surface 160C of the seal housing 160 as illustrated in FIG. 12 and FIG. 13. FIG. 12 and FIG. 13 both show an insertion process in which the stationary seal ring 102 and the gasket 110 are installed in an integrated manner onto the fit engagement surface 160C of the seal housing 160. Members shown in FIG. 12 and FIG. 13 with identical reference numerals to those in FIG. 11 are omitted in their explanations due to their identical arrangement. When the integrated unit of the stationary seal ring 102 and the gasket 110 is fittingly mounted onto the fit engagement surface 160C of the seal housing 160, the thrust end portion 110A of the gasket 110 is urged by means of a force “P” against the fit engagement surface 160C so as to insert the stationary seal ring 102 together with the gasket 110. Under this circumstance, the second rubber layer 110D disposed in the outer circumferential side of the gasket 110 is subjected to shear strain due to a frictional force against the fit engagement surface 160C during the insertion process. Therefore the second rubber layer 110D undergoes elastic deformation such that cross section thereof is deformed to a parallelogram along the direction of insertion. Metal end portion 111A of the reinforcement annulus 111, however, comes to abut the support surface 160A which hampers further advance of the gasket 110. When the external force “P” is removed under this circumstance, the second rubber layer 110D tries to restore its rectangular form due to a spring back force “F” as shown in FIG. 11 or FIG. 13, thereby creating a clearance gap between the support surface 160A and the back surface 102B/ rubber end portions 110B. This clearance gap cannot be visually recognized by assembly workers and remains unknown about its presence from the outboard side “A”.
In the assembled state of the stationary seal ring 102 as shown in FIG. 11 or FIG. 13, if there exists even a small clearance gap between the back surface 102B and the support surface 160A while the stationary seal surface 102A of the stationary seal ring 102 and the rotary seal surface 120A of the rotary seal ring 120 are kept in a seal-tight contact to each other, the stationary seal surface 102A of the stationary seal ring 102 which is urged by spring or fluid pressure via rotary seal ring 120 suffers from a random fluctuation according to the intensity of the pressure. Therefore this may cause a occasional failure of the seal-tight contact between the stationary seal surface 102A of the stationary seal ring 102 and the rotary seal surface 120A of the rotary seal ring 120, thereby leading to degradation of seal performance.
Also when a clearance gap is created between the back surface 102B and the support surface 160A, frictional heat generated on the stationary seal surface 102A of the stationary seal ring 102 is less transferred to the support surface 160A side of the seal housing 160, thereby accelerating accumulation of the heat in the stationary seal ring 102. As the result, the stationary seal surface 102A of the stationary seal ring 102 undergoes deformation due to thermal stress and finds it difficult to maintain a seal-tight contact with the rotary seal surface 120A. And besides, since the accumulated heat is transferred from the stationary seal ring 102 to the gasket 110, the beat causes a fatigue of the rubber-made gasket 110, and is apt to degrade a seal performance for sealing between the seal housing 160 and the stationary seal ring 102.
Patent Reference 1: Japanese Laid-open Utility Model No. H5-1075 (see FIG. 3)